Electroluminescent display system including a preselectably applied low resistance material means

ABSTRACT

An electroluminescent display system comprising a laminated structure with an electroluminescent layer which is energized to emit light in a pattern by means of an applied electric field and a preselectably applied, low-resistance material means.

United States Patent lnventors Norio Suzuki Kawasaki-shi; Tadao Kohashi,Yokohama, Japan Appl. No. 786,248 Filed Dec. 23, 1968 Patented Mar. 23,1971 Assignee Matsushita Electric Industrial Co. Ltd

Osaka, Japan Priority Dec. 28, 1967 Japan 43/127 ELECTROLUMINESCENTDISPLAY SYSTEM INCLUDING A PRESELECTABLY APPLIED LOW RESISTANCE MATERIALMEANS 12 Claims, 3 Drawing Figs.

Int. Cl 1105b 33/26 Field ofSearch 313/108 [56] References Cited UNITEDSTATES PATENTS 3,012,164 12/1961 Franzone et a1. 313/108 3,037,1375/1962 Motson 313/108 3,110,836 11/1963 Blazek et a1. 313/108 3,274,4199/1966 Roth 313/108 3,280,370 10/1966 Nehrich et a1 313/108X 3,325,6646/1967 Buck et 31 313/108 3,344,269 9/1967 Brown 313/ 108K 3,348,05610/1967 Kohashi 313/108X Primary Examiner-Roy Lake AssistantExaminer-Palmer C. Demeo Attorney-Stevens, Davis, Miller & MosherABSTRACT: An electroluminescent display system comprising a laminatedstructure with an electroluminescent layer which is energized to emitlight in a pattern by means of an applied electric field and apreselectably applied, low-resistance material means.

PATENTEU MR2 3 IBTI SHiET 2 [IF 2 ELECTROLUMINESCENT DISPLAY SYSTEMrncwnmo A PRESELECTABLY APPLIED LOW, RESISTANCE MATERIAL MEANS Thisinvention relates to an electroluminescent display system which uses anelectroluminescent element such as an electroluminescent element whichemits light in proportion to the applied electric field intensity.

When a letter or figure is displayed luminously by means of aconventional electroluminescent display system which uses anelectroluminescent element, at least one electrode is formed into ashape of the letter or figure to be displayed and a voltage is fed tothis electrode by some means to display the letter or figure. Therefore,when a complex letter or figure which is separated and not continuous isto be displayed, feeders must be connected to all the separatedelectrodes for the respective separated parts of the letter or figure,and not only the construction becomes very complicated but also itbecomes very difficult to make the electrodes corresponding to theletter or figure to be displayed.

The principal object of the present invention is to provide anelectroluminescent display system which can simply display any letter orfigure by using an electrode having gaps composed of fine metal wiresarranged in parallel or reticulately as the feeding electrode and can beused in many applications by utilizing a flexible thin film sheet asbase plate.

The display system according to the present invention has electrodes forapplying a voltage to a luminescent element which emits light inproportion to the applied field intensity, one electrode of which ismade such an electrode that has gaps and becomes the feeder to aconductive material acting as an electrode provided between the gaps,and any letteror figure can be simply displayed luminously by formingthe conductive material corresponding to the letter or figure to bedisplayed between the electrode'having gaps in electrical contact withthe electrode, and-even when there are many portions to be madeluminescent separately it is sufficient to form the conductive materialat those portions and there is no need to form many feeders separately,whereby the construction of the system becomes very simple.

Furthermore, the display system according to the present invention canbe formed very thinly and flexibly since the base plate is constructedby a flexible thinfilm sheet such as Mylar (trademark for polyethyleneterephthalate) film, the handling of which is easy, and since it isexchangeable with usual recording paper it can be used as the recordingpaper of an X- Y recorder wherein the recorded figure can be displayedluminously by means of the above-described principle, thus the use ofthe system can be extended.

Other objects, features and advantages of the present invention will bereadily apparent from the following detailed description taken inconjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of an embodiment of theelectroluminescent system according to the present invention:

FIGS. la and lb illustrate the feeding electrode distribution thereof.

Referring to the FlGS., the reference numeral 1 represents a resin layercomposed of a dielectric layer of a large resistivity, 2 an electrodehaving gaps which is composed by arranging metal wires, 3 a supportercomposed of a flexible film sheet, 4 an electroluminescent layer such asan electroluminescent layer which emits light in proportion to theapplied electric field intensity, 5 a plate electrode formed by vacuumevaporation of a metal such as Al on the electroluminescent layer 4 and6 an AC power source.

in a case of AC operation, the electroluminescent layer 4 is a layer ofa powder of zinc sulfide activated by copper or aluminum, which powderis mixed into a plastic binder such as a urea resin laminated into athickness of about [.L, which emits light of green color by theapplication of an AC electric field, and the output of the emitted lighthas the character to change nonlinearly in proportion to the intensityof the AC electric field.

The resin layer 1 iscomposed of, for example, epoxy resin and the layer1 must be transparent to the emitted light from the electroluminescentlayer 4. The electrode 2'is formed by arranging tungsten wires having adiameter of about 10 p. in parallel at equal intervals of about I00 t.The intervals of arrangement of wires need to be as narrow as possiblein order to display very small complex letters or figures, but theintervals are desired to be larger than the thickness of the layerbetween the electrodes 2 and 5 in order to make the light emitted whennothing is displayed, that is, dark emission small. it is also desirableto use metal wires as fine as possible in order to make the darkemission small.

The electrode having gaps 2 can also be formed by evaporating such ametal as Al in the shape of a strip on the resin layer 1 having largeresistivity.

The electrode having gaps 2 can also be reticulate. The reticulateelectrode is formed by arranging fine metal wires to intersect at aright angle with each other, by use of a metal net, or by evaporating areticulate metal film.

The electrode 2 is desirable as feeding electrode when a portion of itprojects on the surface of the large resistivity resin layer 1, but itserves as the feeding electrode when the resistivity of the largeresistivity resin layer 1 changes due to, for example, moisture eventhough it does not project on the surface of the layer.

The supporter 3 is composed of a flexible film sheet constructed, forexample, from the product polyethylene terephthalate sold under thetrademark Mylar. The supporter 3 is preferable when it is composed of amaterial having a large dielectric constant and dielectric strengthsince the supporter itself serves also to increase the dielectricstrength and is transparent to the emitted light from theelectroluminescent layer 4 when the evaporated plate electrode 5 isopaque to the emitted light from the electroluminescent layer 4. Theplate electrode 5 is generally formed by evaporating a metal such as A1onto the electroluminescent layer 4, but it is preferable to make theplate electrode 5 transparent to the emitted light from theelectroluminescent layer 4 by evaporating such elements as Au.

Now, the principle of operation of the embodiment of theelectroluminescent system will be described with reference to theaccompanying drawing.

A voltage is applied between the electrodes 2 and 5 from the voltagesource 6 through lead wires. In this case, it is probable that theelectroluminescent layer 4 emits only a small amount of light since theelectric field is applied to the portion of the electroluminescent layer4 where the electrode having gaps 2 exists; the emitted light is verysmall as a whole so that it can be ignored when the electrode is formedby wires having a diameter of about 10 p. thick at intervals of about p.and the sum of the thickness of the electroluminescent layer 4 and ofthe large resistivity dielectric layer 1 is made about 60 11.. Inelectrode practice the emitted light is hardly detected. Electrode 2serves only to supply a voltage and not as an electrode which directlyoperates the electroluminescent layer 4.

When a liquid having low insulation resistance such as water is droppedon the surface of the large-resistivity dielectric layer 1 afteradjusting the applied voltage so that the emission of theelectroluminescent layer 4 hardly takes place and at least a portion ofthe liquid is made to contact the electrode 2, the electric potentialincreases in the direction along the surface of the large-resistivitydielectric layer 1 with respect to the potential of the electrode 2since the surface conductivity in the direction along the surface of thelayer between the electrode 2 is increased. The electric field intensitywithin the electroluminescent layer 4 corresponding to the position ofthe drop also increases, with the result that the emission of light atthe position increases. As described above, the portion emits lightwhere the liquid of low insulation resistance such as water is dropped,that is, where letters or figures are drawn by the liquid.

When there is moisture at a portion instead of a material of lowinsulation resistance such as water, the insulation resistance of thesurface of the large-resistivity dielectric layer 1 also decreasesconsiderably due to the moisture, and if at least a portion of the partwhere the insulation resistance decreased was in contact with theelectrode 2, the portion of the elec troluminescent layer 4 where themoisture exists emits light as in the case where a liquid of lowinsulation resistance such as water is dropped.

In order to eliminate the emission at the portion where the liquid oflow insulation resistance such as water is dropped, the liquid is wipedoff with a cloth or the like, and then the surface of thelarge-resistivity dielectric layer 1 is restored to the original stateand the light emission stops.

We claim:

1. A flexible electroluminescent display system comprising: a laminatedstructure of an electroluminescent layer, a plate electrode provided onone side of said layer, a flexible support sheet of dielectric materialprovided on the other side of said layer; an auxiliary foraminouselectrode provided over the outside surface of said support sheet; anelectrical power source coupled between said two electrodes; and meansfor producing a pattern of visual light emission from saidelectroluminescent layer wherein said means comprises a low-resistancematerial applied to preselected portions on said outside surface, saidmaterial being in electrical contact with adjacent portions of saidforaminous electrode.

2. A flexible electroluminescent display system according to claim 1,further comprising a transparent high-resistance dielectric layermounted on the outside of said support sheet, said foraminous electrodebeing carried by said transparent dielectric layer.

3. A flexible electroluminescent display system according to claim 2,wherein said high-resistance dielectric layer comprises a bonding agentof synthetic resin.

4. A flexible electroluminescent display system according to claim 2,wherein said support sheet is transparent.

5. A flexible electroluminescent display system according to claim I,wherein said foraminous electrode comprises a parallelly and closelyarranged fine metal wire electrode formed by vacuum evaporation.

6. A flexible electroluminescent display system according to claim 5,wherein said wire electrode comprises metal wires having a diameter of10 u and an interval of u therebetween, the sum of the thickness of saidelectroluminescent layer and said high-resistance dielectric layer being60 u.

7 A flexible electroluminescent display system according to claim 1,wherein said foraminous electrode is a reticulate electrode.

8. A flexible electroluminescent display system according to claim 1,wherein said plate electrode is constructed of Au.

9. A flexible electroluminescent display system according to claim 1,further comprising means for removing said light emission pattern oflow-resistance material from said plane.

10. A flexible electroluminescent display system according to claim 1,wherein said support sheet is a polyethylene terephthalate sheet.

11. A flexible electroluminescent display system according to claim 1,wherein said electroluminescent layer comprises a powder of zinc sulfideactivated by copper or aluminum which is mixed into a plastic binderlaminated into a thickness of 50;4..

12. A flexible electroluminescent display system according to claim 1,wherein said lowresistance material is a material which is easilyremovable from said outside surface.

2. A flexible electroluminescent display system according to claim 1,further comprising a transparent high-resistance dielectric layermounted on the outside of said support sheet, said foraminous electrodebeing carried by said transparent dielectric layer.
 3. A flexibleelectroluminescent display system according to claim 2, wherein saidhigh-resistance dielectric layer comprises a bonding agent of syntheticresin.
 4. A flexible electroluminescent display system according toclaim 2, wherein said support sheet is transparent.
 5. A flexibleelectroluminescent display system according to claim 1, wherein saidforaminous electrode comprises a parallelly and closely arranged finemetal wire electrode formed by vacuum evaporation.
 6. A flexibleelectroluminescent display system according to claim 5, wherein saidwire electrode comprises metal wires having a diameter of 10 u and aninterval of 100 u therebetween, the sum of the thickness of saidelectroluminescent layer and said high-resistance dielectric layer being60 u. 7 A flexible electroluminescent display systEm according to claim1, wherein said foraminous electrode is a reticulate electrode.
 8. Aflexible electroluminescent display system according to claim 1, whereinsaid plate electrode is constructed of Au.
 9. A flexibleelectroluminescent display system according to claim 1, furthercomprising means for removing said light emission pattern oflow-resistance material from said plane.
 10. A flexibleelectroluminescent display system according to claim 1, wherein saidsupport sheet is a polyethylene terephthalate sheet.
 11. A flexibleelectroluminescent display system according to claim 1, wherein saidelectroluminescent layer comprises a powder of zinc sulfide activated bycopper or aluminum which is mixed into a plastic binder laminated into athickness of 50 Mu .
 12. A flexible electroluminescent display systemaccording to claim 1, wherein said low-resistance material is a materialwhich is easily removable from said outside surface.